Question

An undefined term can ____be used in a theorem. always, sometimes, never

Answer 1

The answer is Sometimes

Answer 2

The correct answer is:

Sometimes.

Explanation:

There are three terms that are considered the "undefined terms" of geometry:  point, line and plane.  These three terms can be used in the proof of a theorem.

Aside from these three terms, any other term we use in a proof must be defined.